1. Field of the Invention
This invention relates to a modified catalyst for stereo-differentiating reduction of carbonyl compounds and a process for stereo-differentiating reduction with the same catalyst.
By the term "stereo-differentiating reduction" is meant stereo chemical reduction by which one of a pair of enantiomers, each having at least one asymmetric carbon atom, is produced selectively, i.e., in an amount larger than that of the other enantiomer. The stereo-differentiating reduction is classified into enantioface- and diastereo-differentiating reductions, by which optical isomers having one asymmetric carbon atom and those having two asymmetric carbon atoms are produced, respectively. The present invention may be said to pertain to stereo-differentiating hydrogenation of carbonyl compounds with a modified catalyst.
2. Description of the Prior Art
One of the coinventors, Mr. Izumi, first proposed stereo-differentiating reduction of amino acids with a heterogeneous catalyst comprising silk and palladium in 1956 and, further, with a heterogeneous Raney nickel catalyst modified with optically active tartaric acid. The inventors have proposed the stereo-differentiating reduction with a heterogeneous modified catalyst in Japanese Patent Publication No. 22,943/1964 and Angew. Chem. Intern. Ed. Engl., 10, 871 (1971). It is taught in these references that acetoacetic acid esters can be reduced with an stereo-differentiating modified catalyst into 3-hydroxybutyric acid esters at a high optical yield. Furthermore, the inventors achieved an extremely high optical yield of 85% at highest, in 1977, in stereo-differentiating reduction of methyl acetoacetate with a modified nickel catalyst.
Some other research on various stereo-differentiating reduction catalysts has been conducted which catalysts originate in the inventor's stereo-differentiating reduction catalysts. For example, Orito et al: Journal of Organic Synthetic Chemical Society (Japan) 34, 236 (1976), ibid. 34, 672 (1976) and ibid. 35, 753 (1977), reported that nickel-platinum group metal-diatomaceous earth catalysts modified with tartaric acid were active for stereo-differentiating reduction, and particularly those which contain palladium as the platinum group metal brought about an optical yield of approximately 90%. These catalysts are, however, not advantageous in the following points. First, the catalysts necessitate special carriers and it is difficult to prepare the catalysts. This fact materially affects the reproducibility of the optical yield. Secondly, a platinum group metal is expensive. Thirdly, the catalysts inevitably cause side reactions which lead to reduction in the chemical yield of the product.